Photodetection is a fundamental process to many sensing and communication applications, and achieving high sensitivity in photon detection is desirable. A highly sensitive detection process employs number-resolving detection of individual photons. Such detection is now possible with various levels of performance for photons of different wavelengths. Photonic detection, however, is far from ideal. Photon-counting detectors suffer from many shortcomings, and at wavelengths beyond about 1.55 micrometers (“μm”), the detectors are not available at all. At telecommunication wavelengths, the detectors are much worse in performance than at wavelengths compatible with silicon-based detectors, which are, in turn, not as good as photomultiplier tubes.
At the relatively low counting rates encountered in single-photon systems, a primary degradation mechanism for 1.55 μm single-photon detectors (“SPDs”) is so-called “dark-counts.” Dark counts mean a spontaneous avalanche of a Geiger-mode biased avalanche photo diode (“APD”) that is the preferred structure for 1.55 μm single-photon detection. Dark counts from these detectors depend on a bias voltage applied to the detector, as does detection efficiency. Typically, one must sacrifice detection efficiency by lowering the Geiger-mode bias avalanche photo diode voltage to obtain a dark count rate low enough for use in single-photon counting applications. A bias point exists that optimizes detection efficiency and dark count. Dark count rates in silicon detectors are generally much lower than in other solid-state Geiger-mode avalanche photo diodes (“GmAPDs”), but further improvements in signal detection capability would provide enhanced detection capability over longer distances.
In many quantum info nation processing applications, the source of quantum signals is operated so as to avoid multi-photon effects. These sources operate at very low mean photon numbers, much less than one. Such low mean photon number signals coupled with low detection efficiency single-photon detectors makes detection even more challenging, and these systems can benefit significantly from enhanced sensitivity detectors. Enhancing the sensitivity of optical detection would be a valuable step in overcoming performance limitations of single-photon detectors at wavelengths commonly used (e.g., 1.55 μm) in telecommunication systems and in other photonic systems such as light detection and ranging systems.
A further area that exhibits sensitivity limitations relates to the use of resonant nonlinear optical biosensors. A particular biosensing application is concerned with identifying an unknown chemical species in solution. A known method for accomplishing this task is to attach a selective molecular sensor to a transducer element that can be read out with an optical signal. High selectivity is obtained by the molecular sensor, to which only a specific species to be detected (the analyte) will bind.
Limitations of these optical signal and chemical detection approaches have now become hindrances for general high sensitivity light detection applications, and for detection of chemical species in low concentrations. Accordingly, what is needed in the art are new approaches that overcome the deficiencies in the current solutions.